LONDON (Reuters) - Arsene Wenger's faith in his three-man Arsenal defence will be sorely tested in the build-up to his side's visit to a goal-hungry Liverpool on Sunday where any soft centre will likely be cruelly punished.

The Frenchman's decision to start the season with a system he introduced at the tail end of the previous campaign has so far looked questionable in a pulsating 4-3 home victory over Leicester City and defeat at Stoke City.

It hardly looked any more secure and although the return of Laurent Koscielny from suspension should bolster his rearguard at Anfield, it would be no great surprise if Wenger reverted to a back four -- his tried and trusted system.

Whatever he decides, a perceived lack of steel in the Arsenal spine will have a Liverpool attack featuring the likes of Sadio Mane, Mohamed Salah and Roberto Firmino licking its lips at the prospect of facing the Gunners.

"Liverpool always concede but, going forward, they will have miles too much for this current Arsenal side," former Gunners midfielder Paul Merson said this week.

In the last three clashes between the sides Liverpool have racked up 10 goals and have not suffered defeat at home against Arsenal for five years.

The likely return of Alexis Sanchez to the Arsenal starting line-up alongside big summer signing Alexandre Lacazette after a delayed start to the campaign gives Arsenal cause for optimism in a game that promises to be another high-scoring affair.

Especially as Liverpool have hardly looked watertight at the back so far this season -- beginning the campaign with a 3-3 draw against Watford in which their defending was shambolic.

Continued uncertainty about Philippe Coutinho's future has been largely disguised by the electrifying form of Mane, but there is no getting away from Liverpool's defensive fraility.

Despite being swept aside by Liverpool in the Champions League playoff in midweek, German club Hoffenheim scored twice at Anfield, underlining the problems manager Juergen Klopp must try to address before the transfer window closes.

Buoyed by their Champions League qualification, Liverpool will start as favourites though as Klopp aims to continue his impressive record against the so-called big clubs.

Last season Liverpool took 20 points from their matches against Chelsea, Tottenham Hotspur, Manchester City, Manchester United and Arsenal -- more than any other club.

Arsenal managed nine, which is why all eyes will be on Wenger's side as they attempt to shed the image of the lightweights amongst the title contenders.

All eyes too will be on Sanchez whose future at the club remains uncertain -- a cause of worry for the fans but not apparently for Wenger who says the Chilean will still be an Arsenal player after the transfer window closes.

"He has always been focused on his job, he loves to play football and I don't think he is too disturbed by all the (external) noises that happen," Wenger said.